A three-year study is proposed to characterize Ascoviruses, a newly discovered group of large, enveloped, double-stranded DNA viruses isolated from insects. With emphasis on studies of two apparently different ascoviruses, isolated respectively from larvae of the nocutid moths, Trichoplusia ni an Spodoptera frugiperda, a series of studies will be carried out to define these viruses in terms of their basic biological and biochemical properties. The specific objectives of the proposed research include the development of techniques for purification of virions, characterization of the virions in respect to the size and conformation of the DNA genome, and analysis of virion structural proteins. Additionally, the gross pathology, histopathology, and cytopathology caused by these viruses in vivo and in vitro will be described. After the virions have been characterized, studies of the relationships of existing isolates will be undertaken using restriction enzyme analysis of viral DNA and Southern blot analysis of DNA homologies. These studies will permit these viruses to be readily distinguished from other enveloped double-stranded DNA viruses, and will provide a basis on which to pursue studies of their molecular biology.